1. Field of the Invention
This invention relates to an automatic document feeder used in an image processing apparatus such as a scanner or copier, an image processing apparatus equipped with the same, an original conveying method, a program for implementing the method, and a storage medium storing the program.
2. Description of the Related Art
Conventionally, there is known an image reading apparatus that is mounted on a copier and capable of reading originals based on both stationary original reading method and moving original reading method. In order to realize moving original reading, this kind of image reading apparatus is provided with an automatic document feeder that automatically conveys an original from an original tray to a sheet discharge tray via a reading position. Moving original reading is a method in which an image on an original is read by means of a read sensor such as a linear CCD when the original passes through the reading position. Further, in this type of image reading apparatus, the original tray and the sheet discharge tray are disposed one upon another, thereby enabling stationary original reading and moving original reading to be implemented using a compact configuration.
There is known an automatic document feeder operable in a double-sided reading mode that is for reading both sides of an original. In the double-sided reading mode, after reading a first side (hereunder, referred to as “front surface”) of an original using the moving original reading method, the surfaces of the original are inverted (hereunder referred to as “surface inversion”) to read a second side of the original (hereunder, referred to as “rear surface”), and the sides of the original are reversed again before the original is discharged, so that the original may be discharged with the orientation equal to that at the time of reading the first side of the original. In the case where both sides of respective originals are read, each original is conveyed so as to pass through the reading position three times.
Further, to enhance the efficiency of double-sided reading operations, the automatic document feeder feeds two original sheets onto a conveying path inside the automatic document feeder.
In order to further enhance the efficiency of double-sided reading operations, the automatic document feeder can operate in a high-speed double-sided mode in which the front surface of the next original is read while a surface inversion and discharge (hereunder, referred to as “non-reading conveyance”) is being performed for the preceding original for which the reading of the rear surface of the preceding original has been completed. In this case, the order of originals passing through the reading position is: front surface of first sheet→rear surface of first sheet→front surface of second sheet→first sheet (non-reading conveyance)→rear surface of second sheet→front surface of third sheet→second sheet (non-reading conveyance)→rear surface of third sheet, . . . , and so forth.
Further, another automatic document feeder is known that is operable in a high-speed double-sided mode only in a case where the length in a conveying direction of the originals to undergo double-sided reading is shorter than a predetermined value. In this mode, before the preceding original passes through the reading position for the third time, the succeeding original is caused to pass through the reading position for the first time (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2000-143104 and the specification of U.S. Pat. No. 6,354,589). When the length of the originals measured in the conveying direction is equal to or greater than the predetermined value, conveying of originals is carried out in a normal double-sided mode such that the succeeding original has passed through the reading position for the first time after the preceding original passed through the reading position for the third time.
To enable conveyance of originals in the high-speed double-sided mode, the above described automatic document feeder has a conveying path length and a driving system that are enough to simultaneously and individually perform non-reading conveyance of the preceding original and reading of the front surface of the succeeding original.
In order to convey originals of different sizes in the high-speed double-sided mode, however, the driving system becomes complicated and the number of motors increases. As a result, costs rise and the apparatus size is increased.
Further, when a bundle of originals in which long length originals and short length originals are mixed are conveyed in the high-speed double-sided mode, conveyance of the originals becomes impossible during the operation and a paper jam (hereunder, referred to as “jam”) occurs. In that case, the user must perform jam processing by removing the sheets in the conveying path, thus inconveniencing the user.